Installed Reader X on Vista Business and sometimes can't open a pdf file from my browser IE (7). Sometimes freezes browser and have to use Task Manager to close. Some times if I open Acrobat 8 and just leave it open this helps, sometimes it doesn't. Can find no common pattern to when I can and can't open the file but never had a problem until I upgraded to Reader X. Have Security settings wide open and pop up blockers off.
Reader X and Acrobat are not supported on the same Windows system. It is known to cause problems some of which you may now be experiencing.
I'm running Acrobat Pro 8.1.7 and Reader X. Just had my first issues today. Started out that I couldn't print from Reader X in Firefox but was still able to print in IE8. Then I couldn't open Reader X or uninstall Reader X. I could repair it, but it had no effect on the problems.
Eventually, I deleted any Adobe process (3 total) that was running from Task Manager, and Reader X began working again. Acrobat works as well right now. (One process was duplicated, and there was another process running as well. Sorry, I was frustrated and didn't take the time to write down what they were.)
I can't give up Acrobat and Live Cycle Designer. And I don't want to give up Reader X. If the issues don't get any worse than occasionally having to delete 2 or 3 processes, I can live with that for a bit while I hope Adobe will resolve these issues at some point. If the problem becomes more complicated, then I guess it's bye bye Reader X unfortunately.